Government declares state of emergency after clashes between police and activists left four people dead and 21 injured.

At least four people have been killed and 21 injured after security forces clashed with demonstrators protesting a planned $4.8 billion gold mine by US-based Newmont in northern Peru.

The latest death came a day after Peru’s government declared a state of emergency on Wednesday in three northern provinces after protests against the mining project turned violent.

Prime Minister Oscar Valdes announced the death at a Lima news conference though without providing details.

A former Roman Catholic priest, Marco Arana, was also arrested hours earlier in Cajamarca, where the emergency was imposed, further inflaming tensions.

Arana, a 49-year-old veteran of anti-mining protests, complained via Twitter that "in the police station they hit me again, punches in the face, kidneys, insults".

Chief local prosecutor Johnny Diaz told The Associated Press that he had designated a prosecutor to investigate Arana's claim.

Diaz said Arana was arrested for organising meetings, an activity prohibited under the state of emergency. He said authorities had not issued any arrest warrants or made any mass arrests on Wednesday.

State of emergency

The state of emergency was imposed late on Tuesday in Cajamarca province and two neighbouring provinces after three people were killed during a violent protest in the region.

A 17-year-old was among those dead, and 15 people were also arrested at the Conga mining project, Cajamarca region prosecutor Esperanza Leon told RPP radio.

More than 1,000 protesters threw stones at government offices in the town of Celendin, and police responded by firing tear gas to disperse the crowd and suspending freedom of assembly to quell clashes, local media reported.

During the scuffle, two police officers were wounded by "guns fired by protesters who were trying to take over Celendin", the interior ministry said in a statement. It accused the demonstrators of committing "criminal acts".

The Peruvian government declared a state of emergency in Cajamarca and two neighbouring provinces and mobilised the military to support police operations.

Protesters say the Conga mining project will pollute the area's lakes and rivers, contaminating water supplies.

The demonstration came after Celendin Mayor Mauro Arteaga was said to have expressed support for the project.

Conga was approved in 2010 by former president Alan Garcia's government. His successor President Ollanta Humala had been a backer of the project but insists potential environmental impacts must be weighed.

The open-pit project, located some 3,700m above sea level, involves moving the water from four lagoons high in the Andes mountains into reservoirs the company would build.